TM 1-4920-446-13 & PCodeExplanationAO-(Assembled byItems with these codes are not to be requested/requisiorg/AVUM Level)tioned individually. The parts that makeAF-(Assembled by up the assembled item must be requisitioned or fabricated andDS/AVIM Level)assembled at the level of maintenance indicatedAH-(Assembled byby the source code. If the 3rd position code of the SM&R codeGS Category)authorizes you to replace the item, but the source code indicates theAL- Assembled by SRA)item is assembled at a higher level, order the item from the higherAD-(Assembled bylevel of maintenanceDepot)XA-Do not requisition an "XA"-coded item. Order its next higher assembly.(Refer to the NOTE below.)XB-If an "XB" item is not available from salvage, order it using the CAGE codeand part number given.XC-Installation drawing, diagram, instruction sheet, field service drawing, that isidentified by manufacturer's part number.XD-Item is not stocked. Order an "XD"-coded item through normal supplychannels using the CAGE code and part number given, if no NSN isavailable.NOTE:Cannibalization or controlled exchange, when authorized, may be used as a source of supply for items with theabove source codes, except for those source coded "XA" or restricted aircraft support items (refer to AR 750-1).(2) Maintenance Code. Maintenance codes tell you the level(s) of maintenance authorized to USE and REPAIRsupport items. The maintenance codes are entered in the third and fourth positions of the SM&R Code as follows:(a) The maintenance code entered in the third position tells you the lowest maintenance level authorized toremove, replace, and use an item. The maintenance codes are entered in the third position will indicate authorization toone of the following levels of maintenance.CodeApplication/ExplanationC-Crew or operator maintenance done within organizational or aviation unit maintenance.O-Organizational or aviation unit category can remove, replace, and use the item.F-Direct support or aviation intermediate level can remove, replace, and use the item.H-General support level can remove, replace, and use the item.L-Specialized repair activity can remove, replace, and use the item.D-Depot level can remove, replace, and use the item.C-3